how can i know about the efficiency of my antenna?

I know how to mesure the gain,the pattern but how can i calculate or mesure the efficiency of an antenna? :( can somebody tell me? thanks!

I attach here efficiency from Balanis second edition.

hi plasma. do you happen to have the chapter about yagi antennas of balani′s antenna theory and design ?
if you do please upload !
thanks a lot

Hi,
you can download Balanis's book compeletly from MCU.CZ (from eirp's uploaded files), with thanks to eirp.

KMPA

There are three sources of loss. One is the resistance of the conductors. This is usually many orders of magnitude less than the radiation resistance and so rarely is a problem.

The second is from radiating power at directions other than the intended one. If the sidelobes are 20 dB down compared to the main beam this only wastes 1% of the power.

The third is reflections from the antenna on the transmission line (SWR). The power goes back down the transmission line and is reflected from the source and goes back to the antenna. This makes the attenuation of the line for this component of power three times ( in dB ) attenuated by the transmission line attenuation.

In practice, Antenna gain,the pattern is more important than efficiency.
mormaly,Only attention the efficiency when antenna gain is low to doubt.

In practice, Antenna gain,the pattern is more important than efficiency.
mormaly,Only attention the efficiency when antenna gain is low to doubt.

No exactly.....An antenna with a gain of 2dB but with an efficiency of
50 % will have a total gain of -1 dB...![/quote]

I think antenna efficiency is very important for small antennas such as the ones on partable devices. Many researchs have been done for acculately estimating radiation efficiency.

Yes, in small antennas, the problem of the efficiency is a very critical problem. There're lot's of reference talking about the topic of efficiency,such as the one in the attachment.And in simulation tools, such as IE3D,you can read the radiation efficiency and antenna efficiency, but as I thought definition of the radiation efficiency and antenna efficiency in IE3D is different from the definition in text book.The difference is in the second attachment.